This invention relates to lamps, and more specifically to arc discharge lamps, such as fluorescent lamps. More particularly, the invention is applicable to arc discharge lamps that require a very precise amount of a substance to be released in the sealed lamp.
Many methods are currently known for supplying mercury to a fluorescent lamp. For example, patents that generally refer to arrangements for introducing mercury into a lamp include U.S. Pat. Nos. 2,415,895; 3,230,027; 3,300,037; 3,764,842; 4,182,971; 4,335,326; and 4,823,047. As disclosed in many of these patents, the most common methods of introducing mercury to a sealed lamp are mechanical dispensing, use of a mercury-containing amalgam, and release of the mercury from a capsule within the fluorescent lamp.
One drawback to the foregoing apparatus and methods includes the necessity for specialized machinery and equipment. Specialized machinery unfortunately has additional costs associated therewith. Still other ones of these arrangements require specialized lamp components to accommodate the mercury releasing structure. Still further, some of these arrangements have the potential for losing some or all of the substance being charged to the lamp during processing, as well as the presence of unwanted impurities being introduced into the lamp.
The use of a capsule sealed inside the lamp to subsequently release a substance such as mercury resolves some of the foregoing problems. U.S. Pat. Nos. 3,794,402 and 3,794,403, for instance, disclose one arrangement of this type wherein a capsule containing mercury is disposed inside the lamp assembly. The capsule is held against a filament or wire. Upon heating of the wire by induction with the assistance of a primary coil located outside of the lamp, the capsule is ruptured and the mercury released. These patents do not, however, address the problem of premature rupture of the capsule or vessel during other manufacturing and processing steps of the lamp which may cause inadvertent heating of the filament or wire and consequently, premature release of the mercury. This particular arrangement in the '402 and '403 patents also requires a primary coil outside of the lamp that must be accurately aligned with the internal release mechanism. Even having achieved such alignment, reliable mercury dosing is not always possible.
It is an object of this invention, therefore, to provide a device whereby release of a specified substance, such as mercury, to a sealed lamp from a capsule or container within the lamp can be controlled.
It is another object of the invention to provide a means whereby a highly accurate dose of a specified substance is controllably released into a sealed lamp.
It is yet another object of the invention to provide a means for controllably releasing a pre-measured dose of a specified substance into a sealed lamp envelope using minimal current and without employing specialized external equipment or expensive, specially configured lamp components.
Still other objects will become apparent to those skilled in the art upon reading this specification and the attached claims and with reference to the accompanying drawings.